1. Field of the Invention
The present invention relates generally to a magnetic head using an amorphous ferromagnetic alloy for a core.
2. Description of the Prior Art
A typical conventional magnetic head uses an alloy such as permalloy, Sendust (trademark) or Alperm (trademark) and ferrite for a core. At present, ferrite is the best of these materials in abrasion-resistance, but ferrite has a lower saturation flux density, BS, by 30-50% than the above-mentioned alloy material. In case that the ferrite magnetic head is applied to recording with a high density magnetic recording medium which has appeared recently and has a high coercive force, the magnetic saturation of the core material is a problem, and its performance is not so good compared with the material of the alloy. On the other hand, the alloy material is not satisfactory in abrasion-resistance in comparison with ferrite, but it is superior in saturation flux density, BS.
An amorphous ferromagnetic alloy which is superior in magnetic characteristic has appeared. However, since it is difficult to make thick material of the amorphous alloy, in order to assemble the core of the magnetic head, the core keeps its mechanical strength by being pinched with a pair of non-magnetic clamping plates on both sides thereof. The technical art of bonding of these materials has become extremely important.
Usually, glass-bonding is used for the ferrite magnetic head, and for the alloy material, a brazing with silver or the like material is adopted, wherein the working temperature is usually over 700.degree. C. As for the amorphous alloy, the working temperature usually must be lower than 500.degree. C. when considering the magnetic characteristic--a crystalization temperature (hereinafter is referred as TX). When the amorphous ferromagnetic alloy is heated over the crystallization temperature, TX, it crystallizes and becomes brittle, and furthermore the magnetic characteristic is deteriorated, and such an amorphous ferromagnetic alloy becomes not usable as the magnetic material. Therefore, in case that the amorphous material is used, bonding of component members of the head core or forming the magnetic gap should be made preferably by bonding the magnetic material with a known epoxy resin or a soldering material. Since the working temperature of these bonding materials is under 300.degree. C., at most, these bonding methods are safe, being free from the crystallization, but there is a shortcoming that the bonding strength is low.
The width of a track in an audio head is comparatively wide and a magnetic gap is wide, too, and therefore, there is no problem of the bonding strength. However, concerning the heads for a video-tape recorder, a computor and a data recorder, their width of a track is very narrow (for example, several tens .mu.m), and the magnetic gap is very narrow too (for example, under 0.3 .mu.m). Accordingly, the present situation is that it is difficult to keep a precise width of the magnetic gap when using bonding or soldering material.
Therefore, as a method to precisely keep the magnetic gap, bonding by glass is the most reliable. However, in case that the magnetic head is composed by using amorphous ferromagnetic metal, the process of bonding and forming of magnetic gap preferably should be carried out under the temperature of 500.degree. C., and a low melting point glass material having a melting point under 500.degree. C. is needed for this process.
A typical conventional low melting point high lead glass has a softening point of 350.degree. C. in view of the bonding strength. This softening point of 350.degree. C. is the lower limit. In order to obtain sufficiently low viscosity for bonding, these bonding glasses must be treated over the temperature of 550.degree. C. However, the amorphous material crystallizes and loses the characteristic of magnetic material even under above-mentioned temperature, and thus the bonding by glass has not been usable. In other words, in case that the core is made from a material of poor heat-resistance such as an amorphous material, there has been a problem that a rigidly bonded magnetic gap could not be formed.